(a) Field of the Invention
The present invention generally relates to an apparatus and a method for removing a dent in sheet metal. More particularly, the present invention relates to an apparatus for removing the dent in sheet metal of an auto body that is coated with non-conductive material having a different thermal expansion coefficient than metal and method thereof.
(b) Description of the Related Art
In general, various induction heating methods such as heating by induction furnace, induction welding, induction cooking, induction sealing have been developed. The induction heating method has advantages of precisely controlling the temperature and location of a heating zone, but is of applicability only to conductive material such as ferrous metal. The automobile repair industry recently began to use the induction heating method in various applications such as removing front windshield and/or rear window and decorative moldings, heating bolt and nuts, and removing minor dents on the sheet metal. Basically, the induction heating method removes the dent of the sheet metal using the fact that only ferrous metal is heated by the electromagnetic field. The sheet metal used in the auto body is generally composed of four layers which are steel panel, paint primer, paint, and clear coat. The paint primer and the paint are relatively thin layers among the four layers. The clear coat, on the other hand, should have enough thickness to endure extreme weather condition. When the auto body is heated by the induction heater, the electromagnetic field induces joule heating on the steel panel through the outer three non-ferrous layers. Then, those outer three layers are heated indirectly by the heated steel panel. Since the thermal expansion coefficient of the steel panel is high, the heated steel panel starts to expand as soon as it is heated. However, there is a short time period between when induction heating is applied and when the clear coat becomes flexible from the indirect heat. Therefore, if the sheet metal is heated circularly around the dented area, the sheet metal is bent toward the clear coat momentarily having tensile force before the heat is transferred from the steel panel, and thus the dent is removed.
In a conventional apparatus for removing dents in auto bodies, the sheet metal is heated by high frequency induction. However, the excessive increase in the temperature of the steel panel causes thermal damage to the clear coat and the paint.
Furthermore, when the heat generated by the high frequency induction is used in the conventional dent remover of the sheet metal, the power of the high-frequency electromagnetic field may cause malfunction of sensors and electronic devices that are mounted near the auto body because the electromagnetic field may cause damage to electronic circuits.
In a conventional induction heating device, a diameter of a wire of the induction coil should be greater than a critical value in order to sufficiently heat the steel panel for removing the dent without damage to the induction coil. If the temperature of the induction coil is decreased, the wire having smaller diameter can be applied to the induction heating device because an electrical resistance of the wire having the same diameter is reduced at a lower temperature of the induction coil.
The above information in this “Background” section is disclosed only to enhance understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.